In a magnetic confinement reactor, a slight alteration in any of the plasma discharge parameters brings the reaction to an immediate halt. There is therefore no risk of runaway. What’s more, the fusion reactor is supplied with a continuous supply of gaseous fuel: if this supply is interrupted, the reaction stops in a fraction of a second.
The ‘nuclear risks’ associated with the use of radioactive tritium1 and the progressive activation of the inner lining of the machine’s vacuum chamber by neutrons have been identified and taken into account both in the design of the machine and in the rules that will apply to its operation and dismantling. The concept of tritium blankets means that the ‘fuel cycle’ is limited to the machine enclosure: this rules out any problems that might arise from the transport of tritium.
Fusion reactors will be classified as ‘Basic Nuclear Installations’ (INB) and, as such, will be subject to oversight by the French Nuclear Safety Authority. The principle of ‘defence in depth’, which applies to all BNIs, will be applied and requires successive containment barriers to be put in place on a fusion reactor.
The fusion reaction, which is very different from the fission reaction, does not produce any elements comparable to ‘fission products’. No high-level, long-lived waste will be produced by fusion reactors. However, very low-level waste (20% of the total volume), short-lived low- and intermediate-level waste (75%) and, in small quantities (5%), long-lived intermediate-level waste will be produced. This waste is only that caused by the activation of the installation itself.
The development of low-activation materials that are resistant to 14 MeV neutrons means that a hundred years after the shutdown of a fusion reactor, the radiotoxicity of the materials that make up the installation will have fallen to a level close to that of natural radioactivity.
1. Tritium has a relatively short half-life of 12.3 years and decays by emitting a low-energy electron: 5 millimetres of air or a single sheet of paper are enough to stop it and it cannot pass through the skin. So it can only damage the body’s cells if it is inhaled or ingested. It is not chemically toxic.